For riders to find the cycling computer useful, it must collect and present its statistics with a minimum of fuss. Ambient temperature and humidity are easily monitored with sensors attached to the cycling computer's housing, but the rider's heart rate presents a special problem.
In its original design, the cycling computer monitored heart rate using either a set of rib cage electrodes or a glove mounted photosensor. Neither of these would be acceptable in a commercial product, because connecting wires between the sensors and the cycling computer could become tangled or impede rider movement.
New foam handlebar grips with integrated foil contacts solve this problem and are readily available, because they are commonly used on stationary exercise bicycles. When gripped by the rider, an EKG signal that can be monitored by the ADC appears across these contacts.
The 16-bit timer input capture function on the MC68HC705P6A provides the information needed to calculate speed and distance traveled. A magnetic switch connected to the input capture pin detects wheel rotations, the number of which is directly proportional to distance traveled. Likewise, speed can be calculated from the number of wheel rotations that occur during a given period of time.